Method and system for electrical coupling to copper interconnects

ABSTRACT

A system and method for providing electrical connection to a copper interconnect through a via hole is disclosed. The copper interconnect includes a surface having impurities. The method and system include chemically reducing the copper oxide and removing the carbon atoms at the surface. The chemical etching is performed using a reactive species. The reactive species reacts with the impurities on the surface of the copper interconnect to remove the impurities.

FIELD OF THE INVENTION

The present invention relates to copper interconnect formation and moreparticularly to a method and system for electrically coupling to copperinterconnects having improved electrical connection and reduced coppercontamination.

BACKGROUND OF THE INVENTION

Typically, a damascene process is used to form interconnects forsemiconductor processing. First, a trench is formed in a dielectric filmon a substrate. A barrier metal is deposited to prevent the copper whichwill form the interconnect from diffusing through the dielectric layer.Subsequently, chemical polishing is performed on the copper interconnectand other layers are formed above the copper interconnect.

In order to provide an electrical connection to the interconnect, a viais used. A via hole is made in the layers above the copper interconnectto expose the copper interconnect. The via hole will be filled with somemetal to provide an electrical connection. However, the surface of thecopper in the interconnect may be oxidized or contain impurities dueprimarily to the chemical polishing. As a result, sufficient electricalcontact cannot be made to the copper interconnect.

Conventional systems, such as those used in aluminum interconnectiontechnology, sputter the surface of the interconnect metal. Sputteringcauses copper and impurity atoms to be ejected from the exposed surfaceof the copper interconnect. Although the sputtering process removes theimpurities from the surface of the copper interconnect, the impuritiesand copper are redeposited on the sides of the via hole. Because copperdiffuses readily, the copper can diffuse through the layers above thecopper interconnect. This diffusion can contaminate any junctions formedon the substrate.

Accordingly, what is needed is a system and method for providingsufficient electrical connection to the copper interconnect withoutintroducing copper impurities to the circuit. The present inventionaddresses such a need.

SUMMARY OF THE INVENTION

The present invention provides a method and system for providingelectrical connection to a copper interconnect through a via hole. Thecopper interconnect includes a surface having impurities. The method andsystem comprises chemically reducing copper compounds at the surface ofthe copper interconnect. The chemical etch etching is performed using areactive species. The reactive species reacts with the impurities on thesurface of the copper interconnect to remove the impurities.

According to the system and method disclosed herein, the presentinvention allows for electrical connection to a via without introducingsignificant copper impurities to other portions of the circuit, therebyincreasing overall system performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a copper interconnect and via hole formedusing a conventional process.

FIG. 1B is a block diagram of a conventional via hole and copperinterconnect.

FIG. 2 is a block diagram of a via hole and copper interconnect inaccordance with the method and system.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improvement in circuit performancethrough formation of vias whose via resistance is low and uniform in achip. The following description is presented to enable one of ordinaryskill in the art to make and use the invention and is provided in thecontext of a patent application and its requirements. Variousmodifications to the preferred embodiment will be readily apparent tothose skilled in the art and the generic principles herein may beapplied to other embodiments. Thus, the present invention is notintended to be limited to the embodiment shown but is to be accorded thewidest scope consistent with the principles and features describedherein.

FIG. 1A is a block diagram of a portion of a circuit 10 formed on asubstrate 11. Typically, the substrate 11 is silicon. A damasceneprocess has used to form an interconnect 16. First, a trench is formedin a dielectric layer 15 on the substrate 11. A barrier metal layer 14is formed to prevent the copper which will form the interconnect fromdiffusing through the dielectric layer. The copper layer is thendeposited to form the copper interconnect 16. Subsequently, chemicalpolishing is performed on the copper layer and a dielectric layer 17 andat least a second layer 19 are formed above the copper interconnect 16.The dielectric layer 17 is typically made of silicon dioxide.

In order to provide an electrical connection to the copper interconnect14, a via is formed. To fabricate the via, a via hole 12 is made in thelayers 17 and 19 above the copper interconnect 16 to expose the copperinterconnect 16. The via hole 12 will be filled with some metal toprovide an electrical connection. The metal in the via may be copper ortungsten. However, the exposed surface 18 of the copper in theinterconnect may be oxidized or contain impurities due primarily toreactants used in the chemical polishing and due to reactants used inthe etching of the dielectric film 17 to open the via. For example, theexposed surface 18 may include oxidized copper and carbon. As a resultof these impurities, sufficient electrical contact cannot be made to thecopper interconnect 16.

Conventional systems, such as those used in aluminum interconnectiontechnology, sputter the surface of the interconnect metal. Typically insputtering, an inert gas such as argon is used. FIG. 1B depicts thecopper interconnect 16 and via hole 12 after sputtering. Sputteringcauses ions of the inert gas, not shown, to strike the exposed surface18 of the copper interconnect. The physical interaction between theinert gas ions causes the oxidized copper and impurity atoms to beejected from the exposed surface 18 of the copper interconnect 16. As aresult, the oxidized copper and impurity atoms are removed from thecopper interconnect 16.

Although an electrical connection can be made through the via hole 12 tothe copper interconnect 14, those with ordinary skill in the art willrealize that the sputtering process causes the impurities and copperatoms, denoted generally at 20, to be redeposited on the sides of thevia hole 12. Note that the number and exact placement of the redepositedcopper atoms 20 are for illustration only. Consequently, any number ofcopper atoms 20 could be redeposited any place in the via hole 12.Because copper diffuses readily, the copper can diffuse through thelayers above the copper interconnect. In particular, the copper atoms 20in the dielectric layer 19 can diffuse through the dielectric layer 19.This diffusion through the dielectric layer 19 can contaminate thecircuits formed on the substrate 11.

The present invention provides for a method and system for allowingelectrical connection to a copper interconnect with reduced introductionof copper impurities to the layers above the copper interconnect. Thepresent invention includes chemically removing the impurities on thesurface of the copper interconnect to allow electrical connection to thecopper interconnect. The present invention will be described in terms ofthe use of hydrogen gas to chemically remove the impurities. However,one of ordinary skill in the art will readily recognize that this methodand system will operate effectively for other species which react withthe impurities on the surface of the copper interconnect.

To more particularly illustrate the method and system in accordance withthe present invention, refer now to FIG. 2 depicting a block diagram ofone embodiment of such a system 100. The system 100 includes a copperinterconnect 116, a barrier layer 114, a via hole 112, dielectric layers115 and 117, and an additional layer 119 formed on the substrate 111. Ina preferred embodiment, the substrate 11 is silicon and the dielectriclayers 115 and 117 are silicon dioxide and silicon nitride,respectively. The dielectric layer 119 is silicon dioxide. In apreferred embodiment, the interconnect 116 and via hole 112 are formedas discussed above, leaving oxygen and carbon impurities on the surfaceof the copper interconnect 116.

Instead of removing the impurities using argon gas sputtering, themethod and system use a gas which chemically reacts with the impurities.In a preferred embodiment, the method and system use hydrogen gas toform the plasma. As a result, a chemical interaction takes place betweenthe oxidized copper and the hydrogen plasma and between the carbon andthe hydrogen plasma. The hydrogen plasma reacts with the oxidized copperto form primarily copper, which remains in the copper interconnect 111,an oxygen-hydrogen radical and water. Similarly, the hydrogen plasmachemically reacts with the carbon. Thus, the hydrogen plasma chemicallyreduces the copper oxide and removes carbon atoms from the surface ofthe copper interconnect 116 through reduction. Consequently, copperatoms remain in the copper interconnect 116 and cannot be found on theside surfaces of the via hole 112. The via hole 112 can then be filledwith copper to electrically couple to the copper interconnect 116without introducing copper impurities which may diffuse through thedielectric layer 117.

A method and system has been disclosed for providing electricalconnection to a copper interconnect with reduced copper contamination.

Although the present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments and thosevariations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method for providing electrical connection to acopper interconnect through a via hole, the copper interconnectincluding a surface having impurities, the method comprising the stepsof:causing a reaction between a reactive species in a plasma and theimpurities on a portion of the surface of the copper interconnectexposed by the via hole to remove the impurities on the portion of thesurface of the copper interconnect; and depositing copper in the viahole.
 2. The method of claim 1 wherein the reaction causing step furthercomprises the step of:reducing copper oxide and reacting with carbonatoms on the surface of the copper interconnect.
 3. The method of claim2 wherein the reactive species further comprises hydrogen gas.
 4. Themethod of claim 1 wherein the reaction causing step further comprisesthe step of:chemically reducing the copper oxide and removing carbonatoms at the surface of the copper.